A femto base station is basically a low cost and low power base station (BS) transceiver which is installed indoors (e.g., in a home or office) and connected to the Internet via cable, DSL, on-premise fiber optic link, or a similar IP backhaul technology. This connection is used to integrate the femto base station with the wireless operator's core network.
A femto base station serves a geographic area known as a femto cell over a single carrier or channel. A femto cell typically covers a smaller geographic area or subscriber constituency than a conventional macro cell. For example, a femto base station typically provides radio coverage in a geographical area such as a building or home, whereas a conventional macro base station provides radio coverage in a larger area such as an entire city or town. The function of a femto cell is similar to that of a Wireless LAN (Local Area Network), and provides operators a low cost solution for extending coverage areas and off-loading users from the cellular network.
In a wireless network including femto cells, upon entering a cell, a mobile station in an idle state (hereinafter an idle mobile station) receives broadcast overhead messages such as a sector-parameters message on the well-known broadcast control channel. In the current 3GPP2 CDMA2000 EVDO standards (e.g., 3GPP2 CDMA2000 EVDO standard “cdma2000 High Rate Packet Data Air Interface Specification,” 3GPP2 C.S0024-B, Ver. 2.0 (March 2007)), a sector-parameters message includes one or more color codes. Such color codes, which are periodically broadcast as a sequence of bits, are used to identify a particular subnet of a communications network.
While in the idle mode, the mobile station periodically monitors (“wakes up” and receives) the broadcast control channel for changes in the received sector-parameters such as color codes. Conventionally, base stations located at a border area of a particular subnet transmit both primary and secondary color codes. The primary color code is the color code associated with the subnet in which the base station or cell resides, whereas the secondary color code identifies the bordering subnet. The broadcasting of the primary and secondary color codes indicates to mobile stations that they are in a border area of a particular subnet.
Broadcasting of primary and secondary color codes by base stations located in each bordering subnet provides spatial hysteresis and suppresses ping-pong effects. In the current EVDO standard, the secondary color code mechanism provides spatial hysteresis preventing any mobile from conducting idle handoff when the mobile is in a border area covered by the secondary color code. In this case, if the secondary color code is applied at the bordering macro cell, relatively slow moving mobiles conduct handoff only after moving out of the bordering macro cell. Because these mobiles move relatively slowly, the period of time required for a mobile to move out of the bordering macro cell may be relatively long. During this period of time (which may be relatively long), the mobiles are not be served by either the femto cells or the macro cell, which may cause unacceptable service interruption.